Drug Possession in Missouri

My question involves criminal law for the state of: Missouri

Me and my ex ..sister in law were driving through Missouri when my car broke down. The cops came and she let them search her purse and she had 8 pills and 2 hits of acid in her purse! I had absolutely no drugs on me whatsoever but they arrested and charged both of us with a class C felony. How hard will it be for me to get the charges dropped? I don't know what my sister in law will say about me in court because of a horrible custody battle i am in with her brother. She may say i planted all the drugs on her for all i know!

Anyone??? lol